In the last few years, the metal working industry has set high standards concerning the quality of cooling lubricants that is used therein.
In addition to good cooling and lubricating properties, these lubricants must provide excellent protection against corrosion, stability against microorganisms, and in those instances where skin contact is unavoidable, the compositions should be nontoxic and dermatologically safe.
In other technical areas of application, where water or aqueous solutions are used in the presence of corrosion susceptible metals or their alloys, there is a constant need for adequate corrosion protection.
In the past, numerous corrosion inhibitors were prepared which have proven to be effective. These include salts or condensation products of mono-, di- or trialkanolamines and boric acid in conjunction with organic acids if needed.
Mixtures of boric acid, unsaturated fatty acids and alkanolamines are known from U.S. Pat. No. 2,999,064. These aqueous solutions are used as cutting fluids and show the best microbiocidal properties. However, there are many disadvantages associated therewith. For example, besides the disadvantage of foaming, the anti-corrosive character of these mixtures is inadequate.
In DE-OS 1620447 and DE-OS 2007229, salts or condensation products of alkanolamines and ortho-boric acid are described as foamless water-hardening nonreactive rust inhibitors with fungistatic and bacteriostatic action. The corrosion inhibiting action of these compositions has proven to be inadequate in practice.
When secondary amines are used, however, it is impossible to exclude formation of nitrosamine because of their reaction with other components in the final aqueous formulation or under conditions of use. Moreover, the toxicity of nitrosamines are well known.
Nitrosamine formation does not occur if primary amines are used. Hence, as described in U.S. Pat. No. 4,022,713, the reaction product of monoalkanolamines having 1 to 3 carbon atoms in the alkanol chain is not problematic in this regard. When used as a rust inhibitor, however, this product does not meet the demands of practical applications. Additionally, when used as cutting oils or as a cooling lubricant, the adhesiveness of its surface-dried residues has always been troublesome.